add jekyll extlinks

_config.yml

@@ -63,6 +63,10 @@ autopages:
   collections:
     enabled: false
 
+extlinks:
+  attributes: {rel: "noreferrer noopener", target: _blank}
+  rel_exclude: ['angular.de', 'vuejs.de', 'reactjs.de', 'workshops.de', 'webdave.de', 'ng-de.org', 'conf.vuejs.de']
+
 # Build settings
 markdown: kramdown
 sass:

_layouts/post.html

@@ -50,7 +50,7 @@ <h1 class="header-post-title">{{ page.title }}</h1>
         </p>
 
         <div class="c-content">
-          {{ content }}
+          {{ content | extlinks }}
         </div>
 
         <div class="text-end">

_plugins/jekyll-extlinks.rb

@@ -0,0 +1,76 @@
+# Jekyll ExtLinks Plugin
+# Adds custom attributes to external links (rel="nofollow", target="_blank", etc.)
+#
+# Configuration example in _config.yml (notice the indentation matters):
+#
+# extlinks:
+#   attributes: {rel: nofollow, target: _blank}
+#   rel_exclude: ['host1.com', 'host2.net']
+#
+# (attributes are required - at least one of them, rel_exclude is optional)
+# Relative links will not be processed.
+# Links to hosts listed in rel_exclude will not have the 'rel' attribute set.
+# Links which have the 'rel' attribute already will keep it unchanged, like
+# this one in Markdown:
+# [Link text](http://someurl.com){:rel="dofollow"}
+#
+# Using in layouts: {{ content | extlinks }}
+#
+# Developed by Dmitry Ogarkov - http://ogarkov.com/jekyll/plugins/extlinks/
+# Based on http://dev.mensfeld.pl/2014/12/rackrails-middleware-that-will-ensure-relnofollow-for-all-your-links/
+
+require 'jekyll'
+require 'nokogiri'
+
+module Jekyll
+  module ExtLinks
+    # Access plugin config in _config.yml
+    def config
+      @context.registers[:site].config['extlinks']
+    end
+
+    # Checks if str contains any fragment of the fragments array
+    def contains_any(str, fragments)
+      return false unless Regexp.union(fragments) =~ str
+      true
+    end
+
+    def extlinks(content)
+      # Process configured link attributes and whitelisted hosts
+      if config
+        if config['attributes']
+          attributes = Array(config['attributes'])
+        end
+        if config['rel_exclude']
+          rel_exclude = Array(config['rel_exclude'])
+        end
+      end
+      # Stop if no attributes were specified
+      return content unless attributes
+
+      doc = Nokogiri::HTML.fragment(content)
+      # Stop if we could't parse with HTML
+      return content unless doc
+
+      doc.css('a').each do |a|
+        # If this is a local link don't change it
+        next unless a.get_attribute('href') =~ /\Ahttp/i
+
+        attributes.each do |attr, value|
+          if attr.downcase == 'rel'
+            # If there's a rel already don't change it
+            next unless !a.get_attribute('rel') || a.get_attribute('rel').empty?
+            # Skip whitelisted hosts for the 'rel' attribute
+            next if rel_exclude && contains_any(a.get_attribute('href'), rel_exclude)
+          end
+          a.set_attribute(attr, value)
+        end
+      end
+
+      doc.to_s
+    end
+
+  end
+end
+
+Liquid::Template.register_filter(Jekyll::ExtLinks)